The Department for Culture, Media and Sport has acknowledged that is has received the letter, and said it will respond to the NSPCC, but is yet to do so publicly.

The social network responded by saying that they believe that raising awareness of the video may help to identify those involved.

The social network has a policy whereby it allows discussion of sensitive issues as long as it does not promote them.

The NSPCC's chief executive, Peter Wanless, said it is time for "the light to be shone on the responsibilities of social media companies", adding that it is an area where progress has been "extremely slow".

In a statement, Facebook said: "Like others, we find the behaviour in this video upsetting and disturbing. In cases like these, we face a difficult choice: balancing people's desire to raise awareness of behaviour like this against the disturbing nature of the video.

"In this case, we are removing any reported instances of the video from Facebook that are shared supporting or encouraging this behaviour.

"In cases where people are raising awareness or condemning the practice, we are marking reported videos as disturbing, which means they have a warning screen and are accessible only to people over the age of 18."

In the NSPCC letter, which was sent to minister for internet safety and security Joanna Shields and culture minister Ed Vaizey, Mr Wanless said the NSPCC has received complaints in recent weeks about other images posted on Facebook which apparently showed the blanket-covered corpse of a baby lying in a pool of blood and a woman hitting a boy with a stick and kicking him.

Referring to the video, he wrote: "We are obviously extremely concerned for the welfare of the infant and are urging Facebook to offer every co-operation with the authorities to try and track down this callous individual and protect the baby.

"While the welfare of this child is naturally paramount, we would also urge you to look at all available options which will ensure UK citizens, including millions of children, are no longer exposed to this kind of dreadful and disturbing content.

"The NSPCC believes we have now reached the long-overdue point where it is time for social networking sites to be held to account for the content on their sites and pay more attention to their safeguarding duties to protect children and young people, whether they are viewing the content or appearing in it.

"Our judgment is that when this issue is being shared to draw attention to it and condemn what is happening, and ideally to try and help this child and rescue the child, then yes, there is a place for it on Facebook," he said.

"If it was being shared to praise it or to make fun of it, absolutely not, and we will take it down.

"Our response has been yes, it does not breach our terms, but it is a disturbing and distressing video ... and therefore it is right that we put up a warning.

"There is a warning on the video and again only if it is shared in the context of condemning, that explains it is disturbing and therefore people can choose if they wish not to view it."

An NSPCC spokeswoman said the warning went on the video only after the charity had drawn attention to it.

Mr Milner insisted the site "reacts very quickly" to complaints about content.

"We have very extensive reporting mechanisms on Facebook to enable people to let us know what is happening. And we have an expert team who are handling millions of reports every week in more than two dozen languages," he said.

Mr Milner said they had decided a video of a woman being beheaded should be taken off the site after David Cameron complained.

"These decisions are often very difficult," he added.

"This happens in news programmes as well. People will broadcast really quite distressing scenes with warnings to draw attention to what is going on in the world. We are making those judgments all the time."

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